Structure of aluminum atomic chains

First-principles density-functional calculations reveal that aluminum can form planar chains in zigzag and ladder structures. The most stable one has equilateral triangular geometry with four nearest neighbors; the other stable zigzag structure has wide bond angle and allows for two nearest neighbors. An intermediary structure has the ladder geometry and is formed by two strands. While all these planar geometries are more favored energetically than the linear chain, the binding becomes even stronger in nonplanar geometries. We found that by going from bulk to a chain the character of bonding changes and acquires directionality. The conductance of zigzag and linear chains is 4e²/h under ideal ballistic conditions.